Prop shaft split coupling - through bolt needed?

[JimC]

I have removed the prop shaft to enable replacement of the cutless bearing. The coupling to the Yanmar 2GM20F is the split type with the 25mm shaft clamped by pinch bolts each side of the split. There is a small (6mm?) hole drilled on a diameter through both halves of the coupling and the shaft. Should there be a bolt or anything through this or is the clamping action alone sufficient. I found a bit of broken studding in the hole through the shaft.

 

[sailor211]

Clamping should be enough, although I have had a prop shaft slide back after more than a seasons use!! luckily the shaft hit the rudder and shaft and prop was not lost!!

Since then I have pit a bolt through.

 

[Georgio]

I have removed the prop shaft to enable replacement of the cutless bearing. The coupling to the Yanmar 2GM20F is the split type with the 25mm shaft clamped by pinch bolts each side of the split. There is a small (6mm?) hole drilled on a diameter through both halves of the coupling and the shaft. Should there be a bolt or anything through this or is the clamping action alone sufficient. I found a bit of broken studding in the hole through the shaft.

I have the same type of clamp and have never had a problem with the shaft slipping or pulling out.

 

[Marsupial]

I had one fitted last year and was advised to have a keyway machined in it and the shaft to stop them turning, and have a couple of jubilee clips on the propshaft so the shaft wont go IF it should fall out of the coupling. The other solution offered was to drill the coupling and the shaft and insert a roll pin but I could see that being difficult to remove and refit. I opted for the keyway.

As "luck" would have it the day after the boat was launched we noticed a drip from the stern gland and decided to change it afloat, it all came apart easily and went back together easily. Split couplings get my vote.

 

[vyv_cox]

I have removed the prop shaft to enable replacement of the cutless bearing. The coupling to the Yanmar 2GM20F is the split type with the 25mm shaft clamped by pinch bolts each side of the split. There is a small (6mm?) hole drilled on a diameter through both halves of the coupling and the shaft. Should there be a bolt or anything through this or is the clamping action alone sufficient. I found a bit of broken studding in the hole through the shaft.

This type?

Mine has a grub screw, on the other side in the photo, that engages with a dimple in the shaft. Prevents slippage and easy to remove.

 

[JimC]

This type?

Not quite like that but similar, and connecting direct to the gearbox output shaft without the flexible coupling. Mine is the standard coupling fitted to thousands of Yanmars. The grub screw into a dimpled shaft sounds good but I've no engineering facilities to enlarge and tap the hole in the coupling with sufficient accuracy.

 

[Spyro]

I have a similar set up with split coupling but I have a tapped hole in the coupling which takes a bolt which meets with a dimple in the shaft.
If you can get the stud out of the shaft I would replace it with a new bolt, it's obviously what the holes were there for. If you don't replace it you'll be forever checking that the shaft is still locked in place.

I've often wondered whether the bolt I have would create an imbalance in the shaft and coupling set up.

 

[vyv_cox]

Not quite like that but similar, and connecting direct to the gearbox output shaft without the flexible coupling. Mine is the standard coupling fitted to thousands of Yanmars. The grub screw into a dimpled shaft sounds good but I've no engineering facilities to enlarge and tap the hole in the coupling with sufficient accuracy.

Not much needed so far as engineering is concerned. You need a set of taps for the size of grub screw chosen, 5 mm would be reasonable. You then need a drill of the correct size, 4.2 mm according to the table here. Any decent tool shop would stock them.

Drilling with a handheld electric drill would be perfectly OK. Look at the Metric Taps page on the same website, you will see that they come in threes. The first one to use is the most tapered one, then the next. Offer it up to the hole ensuring it is square to the coupling, fore and aft and side to side. Oil the tap, then turn gently, turning it back every half turn or so to break off the swarf.

Simples!

 

[Tranona]

Clamping the bolts up should be enough. Usually the problem is getting the coupling off rather than coming loose. Only reason why I can think of anybody drilling through is if the shaft is 25mm and the coupling is 1 inch. But if it has been working OK without the pin just clamp it back up.

 

[Spyro]

Not much needed so far as engineering is concerned. You need a set of taps for the size of grub screw chosen, 5 mm would be reasonable. You then need a drill of the correct size, 4.2 mm according to the table here. Any decent tool shop would stock them.

Drilling with a handheld electric drill would be perfectly OK. Look at the Metric Taps page on the same website, you will see that they come in threes. The first one to use is the most tapered one, then the next. Offer it up to the hole ensuring it is square to the coupling, fore and aft and side to side. Oil the tap, then turn gently, turning it back every half turn or so to break off the swarf.

Simples!

Or if you don't have a set of taps take the whole lot to a small enginnering firm, with cash in your pocket you'd get it done for less than the price of the taps